The Incidence of Spontaneous Abortion in Mothers with Blood Group O Compared with other Blood Types.

Although ABO incompatibility between mother and fetus has long been suspected as cause of spontaneous abortion in man, its precise contribution has not been completely resolved. In spite of reports in which the incompatible mating was recognized to be a cause of habitual abortion, and which eventually results in infertility or a reduction in the number of living children compared with the number in compatible matings, such effects were not observed in other studies. The aim of this review article was to show some evidence of relationship between ABO incompatibility and spontaneous abortion.

n 1900 Karl Landsteiner reported a series of tests, which identified the ABO blood group system. This is the only blood group in which antibodies are constantly, predictably, and naturally present in the serum of people who lack the antigen. ABO compatibility between mother and fetus is crucial (1).

Abortion
Spontaneous abortion also known as miscarriage, refers to a pregnancy that ends spontaneously before the fetus has reached a viable gestational age (2)(3)(4).

Relationship between ABO Blood Group and Spontaneous Abortion
Sixty-two articles in relation to ABO incompatibility and abortion have been published so far and one of the latest was published in 2011.
Shortly after the ABO blood groups were discovered, attention was directed toward the possibility of harmful effects when mother and fetus have different blood groups. As early as 1905 A. Dienst suggested that toxemia of pregnancy might be due to the transfusion of ABOincompatible fetal blood into the mother. This was not substantiated, and the problem of ABO interaction between mother and fetus was largely overshadowed by the more dramatic effects of Rh incompatibility leading to Rh hemolytic disease. During the second half of the 20th century, many papers have been published reporting the spontaneous abortion due to blood group incompatibility and the operation of natural selection in the human ABO blood group system.
The purpose of this article is to review those and conclude whether the spontaneous abortion is a result of incompatible ABO blood group or not.

Materials and Methods
We have searched the keywords "spontaneous abortion", "ABO blood group" and "incompatibility" in two scientific databases; Pubmed and Google scholar. We limited the search to articles published from 1950 till now. Then the articles were sorted by relevance to the subject.
Most relevant papers were chosen to be reviewed.

Group and Spontaneous Abortion
In showed that the incompatible conspectuses were more likely to be aborted than the compatible ones (5).
The method used in this study is a more powerful method of analysis than simply determining the ABO status of the parents, because an ABO incompatible mating does not necessarily produce an ABO incompatible fetus (6). In the same year, Clarke studied the practical effects of blood group incompatibility between mother and fetus, named early abortion as an effect of blood group incompatibility and mentioned that there is no doubt that ABO incompatibility between early abortuses and the mother is a factor in causing abortion (6).  Finally, it is concluded that the ABO incompatibility between the couples is likely to be a risk factor for early spontaneous abortions and also the heterozygote selection of ABO blood group genotypes (14).

Blood group incompatibility is more frequent in couples with recurrent abortion than fertile couples
Blood group antigens are markers on surface-exposed red cell proteins or the sugar moiety of glycoproteins or glycolipids (15)(16)(17). both enzymes act and make blood group AB with two antigens (18)(19)(20)(21)(22).
Blood groups study revealed that an incompatibility of the blood groups can influence reproduction. Moreover, the mortality of mothers in pregnancy was considerably higher in couples who had blood group incompatibility (23).
The widely repeated delivery of abnormal newborn and stillbirth were more frequent in couples with incompatible blood group than others (24). Infertility could occur in couples with incompatible blood groups (25). However, some studies disagreed with this idea (26). Acceptance of the fetus, which expresses paternally inherited alloantigens by the mother during pregnancy is an exclusive example of how the immune system alters a destructive alloimmune response to a state of tolerance (27)(28) (34)(35).

ABO incompatibility occurs in 20% of
pregnancies, but only 20% of these develop hemolytic disease which is milder than Rh incompatibility and can lead to abortion in the uterus (36)(37)(38).
The blood groups are different, an A mother and an O father will be ABO-compatible, but an O mother and an A father will be defined as an ABO incompatible mate. A further complication is that a  (39).

Conflict of interest:
None declared.